1. Field of the Invention
The present invention is directed to a loop antenna device which generates two different magnetic fields, and in particular to the structural improvement of a loop antenna which has two antennas for generating thereat two different or orthogonal magnetic components, respectively.
2. Related Prior Art
One of the conventional loop antenna devices is disclosed in German Patent Publication DE 4105826. The conventional loop antenna device includes a first antenna A1 and a second antenna A2. The first antenna A1 has a coil L2 wound around a ferrite rod or bar B and a resonant capacitor C2 connected thereto in parallel which constitutes a parallel resonant circuit. The second antenna A2 has a circular coil L1 accommodating therein the ferrite bar B and a resonant capacitor C1 connected in parallel to the circular coil L1 which constitutes a parallel resonant circuit. The ferrite bar B is also wound with a coil L3 to which an amount of current is fed from a power source S.
In the foregoing structure, the ferrite bar B is rotated through an angle .theta. so as to establish a magnetic coupling between the first antenna A1 and the second antenna A2.
Thus, an equivalent circuit shown in FIG. 7(B) can be established in accordance with the resultant condition of the loop antenna device, and a magnetic field component Hz generated by the coil L1 makes an angle, of 90 degrees relative to a magnetic field component Hy generated by the coil L2. It is to be noted that the magnetic field component Hz, the magnetic field component Hy and a magnetic field component generated by the coil L3 extend in the z-direction, y-direction, and x-direction, respectively.
In another conventional loop antenna device which is disclosed in Japanese Patent Laid-open Print No. 10(1998)-51225, a pair of spaced loop antenna each of which is formed of a coil-wounded ferrite bar are arranged between two metal plates in such a manner that a shield plate is interposed between the loop antennas which cross each other at right angles.
However, in the former conventional loop antenna device the inclined condition of the ferrite bar B relative to the circular coil L1 or the angle .theta. therebetween has to be kept for continuous electromagnetic coupling of the first antenna A1 and the second antenna A2. This requires a fixing means for each antenna, resulting in that the structure of the loop antenna device per se becomes complex. In addition, dead spaces are defined between the ferrite bar B and the circular coil Li by which a miniaturization of the loop antenna per se gets difficult.
In the latter conventional loop antenna device wherein both loop antennas cross at right angles, devices such as an a R-C circuit and transformer for establishing a phase difference of 90 degrees between magnetic components generated at both loop antennas are required, resulting in that the loop antenna device per se becomes large and complex in structure.